This invention relates an exhaust gas recirculation mechanism for an engine with a turbocharger.
In an engine with a turbocharger, it has been impossible to recirculate part of the exhaust gas into the engine to decrease the NOx in the exhaust gas without passing it through a compressor of the turbocharger since the exhaust pressure of the engine is lower than the suction pressure of the engine. It is known, however, to recirculate the exhaust gas by introducing part of the exhaust gas into an inlet of the compressor, and to recirculate by introducing the exhaust gas into a suction pipe of the engine using a pump for pressurizing the exhaust gas. The latter case is shown by Automobile Technology Vol. 26, No. 2, 1972 "Recent Survey on Controlling Exhaust Emission and Noise from Diesel Engines" P. 137.
In the exhaust gas, black smoke and corrosive gas are included, and, particularly in the diesel engine, a large quantity of black smoke and corrosive gas are exhausted. Therefore, when these gases are introduced into the pump or compressor, the black smoke or carbon and the corrosive gas adhere to the blades and rotating portions of the pump or the compressor so that its long life time can not be expected.
Further, in a diesel engine with a conventional exhaust gas recirculation mechanism, every time the accelerator is stepped on abruptly a large amount of NOx is discharged for a moment so that the total amount of NOx discharged during running of the engine may be large and can not be disregarded.